HP OpenVMS Systems Documentation

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HP OpenVMS DCL Dictionary

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Closes a mounted disk or tape volume for further processing and deletes the logical name associated with the device.

Requires the GRPNAM (group logical name) and SYSNAM (system logical name) privileges to dismount group and system volumes.


DISMOUNT device-name[:]



Name of the device containing the volume---either a logical name or a physical name. If a physical name is specified, the controller defaults to A and the unit defaults to 0.

If the volume currently mounted on the device is a member of a disk or tape volume set, all volumes in the set are dismounted, unless the /UNIT qualifier is specified.


The DISMOUNT command (which invokes the $DISMOU system service) checks for conditions that prevent a Files-11 volume from dismounting. The conditions fall into the following categories:
  • Installed swap and page files
  • Installed images
  • Devices spooled to the volume
  • Open user files (any files not falling into one of the first three categories)

If the DISMOUNT command does not find any of these conditions, it performs the following operations:

  • Removes the volume from the user's list of mounted volumes, deletes the logical name (if any) associated with the volume, and decrements the mount count.
  • If the mount count equals zero after being decremented, the DISMOUNT command marks the volume for dismounting.
    As soon as the volume is idle, that is, after the DISMOUNT command has determined that no user has any open files on the volume, the DISMOUNT command marks a Files-11 volume for dismounting, and dismounts the volume soon.
  • If the mount count does not equal zero after being decremented, the DISMOUNT command does not mark the volume for dismount (because the volume must have been mounted shared). In this case, the total effect for the issuing process is that the process is denied access to the volume and the logical name is deleted.
  • After a volume is dismounted, nonpaged pool is returned to the system. Paged pool is also returned if the volume was mounted using the /GROUP or /SYSTEM qualifiers.

If the DISMOUNT command does find open files or any other condition that prevents the volume from dismounting, it does not mark the volume for dismounting. Instead, the DISMOUNT command displays a message indicating that the volume cannot be dismounted, followed by messages indicating the conditions that exist and the number of instances of each condition.

The /OVERRIDE=CHECKS qualifier allows a volume to be marked for dismounting despite open files or other conditions. For example, marking a volume for dismounting prevents any new files from being opened. Also, when a volume is marked for dismounting, file-system caches are flushed. This activity is especially important when the system is shutting down and the file-system caches must be written to the disk.

If a volume is part of a Files-11 volume set and the /UNIT qualifier is not specified, the entire volume set will be dismounted.

If the volume was mounted with the /SHARE qualifier, it is not actually dismounted until all users who mounted it dismount it or log out; however, the DISMOUNT command deletes the logical name associated with the device.

If the device was allocated with an ALLOCATE command, it remains allocated after the volume is dismounted with the DISMOUNT command. If the device was implicitly allocated by the MOUNT command, the DISMOUNT command deallocates it.

If the volume was mounted with the /GROUP or the /SYSTEM qualifier, it is dismounted even if other users are currently accessing it. The GRPNAM and SYSNAM user privileges are required to dismount group and system volumes, respectively.



Requires volume ownership or the user privilege VOLPRO (volume protection) to use this qualifier with a volume that was mounted with neither the /GROUP nor the /SYSTEM qualifier. Additionally requires the user privilege SHARE if the volume is mounted privately by a process other than the process issuing the DISMOUNT command.

Specifies that the volume is to be dismounted, regardless of who mounted it. The primary purpose of the /ABORT qualifier is to terminate mount verification. The DISMOUNT/ABORT command also cancels any outstanding I/O requests. If the volume was mounted with the /SHARE qualifier, the /ABORT qualifier causes the volume to be dismounted for all of the users who mounted it.


Dismounts a volume throughout a mixed-architecture OpenVMS Cluster system. If you specify DISMOUNT/CLUSTER, the DISMOUNT command checks for open files or other conditions that will prevent a Files-11 volume on the local node from dismounting. If the DISMOUNT command does not find any open files or other conditions, it checks for conditions on all other nodes in the OpenVMS Cluster. If the DISMOUNT command finds one of the conditions on any node, it displays an error message identifying the device and the nodes on which the error occurred, followed by an error message indicating open files or other conditions on the volume.

After the DISMOUNT command successfully dismounts the volume on the local node, it dismounts the volume on every other node in the existing OpenVMS Cluster environment. If the system is not a member of a cluster, the /CLUSTER qualifier has no effect.


Expels a named shadow set member from the shadow set.

If connectivity to a device has been lost and the shadow set is in mount verification, you can use the /FORCE_REMOVAL ddcu: to immediately expel a named shadow set member (ddcu:) from the shadow set. If you omit this qualifier, the device is not dismounted until mount verification completes.

Note that you cannot use this qualifier in conjunction with the /POLICY=MINICOPY (=OPTIONAL) qualifier.

The device specified must be a member of a shadow set that is mounted on the node where the command is issued.


Marks a Files-11 volume for dismounting even if files are open on the volume. If you specify DISMOUNT/OVERRIDE=CHECKS, the DISMOUNT command displays messages indicating any open files or other conditions that prevent dismounting, immediately followed by a message indicating that the volume has been marked for dismounting.

This command does not close open files on the device. A device cannot be properly dismounted until either all processes with open files have properly closed them, or the processes have been rundown completely.

A substantial amount of time can pass between the time you enter the DISMOUNT/OVERRIDE=CHECKS command and the completion of the dismount operation. Always wait for the dismount to complete before you remove the volume. (To verify that the dismount has completed, enter the SHOW DEVICES command.) Note that the final phase of volume dismounting occurs in the file system, and all open files on the volume must be closed before the actual dismount can be done. Note also that the file system cannot dismount a volume while any known file lists associated with it contain entries.

By using this command, the device is marked for dismount. This prevents additional processes from opening files on the device while existing open files are closed.


Controls the setup and use of the shadowing minicopy function.

Requires LOG_IO (logical I/O) privilege to create bitmaps.

The exact meaning of the MINICOPY keyword depends on the context of the DISMOUNT command, as follows:

  1. If this is a dismount of a single member from a multi-member shadow set, a write bitmap is created to track all writes to the shadow set. This write bitmap may be used at a later time to return the removed member to the shadow set with a minicopy.
    If the write bitmap cannot be initiated and the keyword OPTIONAL is not specified, the dismount will fail and the member will not be removed.
    If you omit the /POLICY qualifier or if you specify /POLICY=NOMINICOPY, no bitmap will be created.
  2. If this is the final dismount of the shadow set in the cluster, the shadow set is verified to be capable of a future minicopy operation.
    If the shadow set has only one member or is in a merge state, and if OPTIONAL was not specified, the dismount will fail.
    Specifying neither NOMINICOPY nor MINICOPY is the same as MINICOPY=OPTIONAL, as the set will be dismounted regardless of the prior checks.

For additional information, refer to HP Volume Shadowing for OpenVMS.


Dismounts only one volume of a volume set on the specified device. By default, all volumes in a set are dismounted.


Avoid dismounting the root volume of a volume set, because it contains the master file directory (MFD). It may be impossible to access files on a volume set if the MFD is not accessible.



Determines whether the device on which the volume is mounted is physically unloaded. If you specify the DISMOUNT command without the /UNLOAD or the /NOUNLOAD qualifier, the qualifier that you specified with the MOUNT command (either /UNLOAD or /NOUNLOAD) determines whether the volume is unloaded physically.




The MOUNT command in this example mounts the tape whose volume identification is PAYVOL on the device MTA0: and assigns the logical name TAPE to the device. By default, the volume is not shareable. The DISMOUNT command releases access to the volume, deallocates the device, and deletes the logical name TAPE.



The MOUNT command in this example mounts the volume labeled DOC_FILES on the device DKA3. Other users can enter MOUNT commands to access the device. The DISMOUNT command shown in this example deaccesses the device for the process issuing the command. If other users still have access to the volume, the volume remains mounted for their process or processes.



The DISMOUNT command in this example dismounts the volume; the /NOUNLOAD qualifier requests that the volume remain in a ready state.



The MOUNT command in this example mounts PAYROLL, a two-volume set. The DISMOUNT command dismounts only PAYROLL02, leaving PAYROLL01 accessible. Note that because the master file directory (MFD) for the volume set is on the root volume, you should not dismount the root volume (in this case, PAYROLL01) of the volume set.


%DISM-W-CANNOTDMT, $10$DJA100: cannot be dismounted
%DISM-W-INSWPGFIL, 4 swap or page files installed on volume
%DISM-W-SPOOLEDEV, 3 devices spooled to volume
%DISM-W-INSTIMAGE, 7 images installed on volume
%DISM-W-USERFILES, 6 user files open on volume

The DISMOUNT command in this example displays the open files and other conditions that prevent device $10$DJA100 from dismounting.


%DISM-W-RMTDMTFAIL, $10$DJA100: failed to dismount on node SALT
%DISM-W-FILESOPEN, volume has files open on remote node
%DISM-W-RMTDMTFAIL, $10$DJA100: failed to dismount on node PEPPER
%DISM-W-FILESOPEN, volume has files open on remote node
%DISM-W-CANNOTDMT, $10$DJA100: cannot be dismounted

The DISMOUNT command in this example displays messages identifying device $10$DJA100 and nodes SALT and PEPPER on which errors occurred followed by messages indicating open files on the volume.

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